On the rate of injection modeling applied to direct injection compression ignition engines

Modern engine design has challenging requirements toward maximum power output, fuel consumption and emissions. For engine combustion development programs, the injection system has to be able to operate reliable under a variety of operating conditions. Today's legislations for quieter and cleaner engines require multiple-injection strategies, where it is important to understand the behavior of the system and to measure the effect of one injection on subsequent injections. This study presents a methodology for zero-dimensional modeling of the mass flow rate and the rail pressure of a common rail system, constructed from a set of experimental measurements in engine-like operating conditions, for single- and multiple-injection strategies. The model is based on mathematical expressions and correlations that can simulate the mass flow rate obtained with the Bosch tube experiment, focusing on the shape and the injected mass, using few inputs: rail pressure, back pressure, energizing time and so on. The model target is to satisfy two conditions: lowest computational cost and to reproduce the realistic injected quantity. Also, the influence of the rail pressure level on the start of injection is determined, especially for multiple-injection strategies on the rate shape and injected mass. Good accuracy was obtained in the simulations. The results showed that the model error is within the 5%, which corresponds at the same time to the natural error of the injector and to the accuracy of the measures which had been done. The benefits of the model are that simulations can be performed quickly and easily for any operation points, and, on the other hand, that the model can be used in real-time on the engine test bench for mass estimations when doing additional experiments or calibration activities.